So as an update, I bought a solid core interior door, 1 3/4" thick, mounted on an exterior door frame (so it came with weatherstripping and an oak threshold). I went to put the door in the other day with a carpenter, and guess what? It was too damn tall. So I am having it resent to the manufacturer to have it cut down to size. I havent figured out yet exactly how much I want to take off the door and jambs, so I seek anyone's input.
oak threshold.jpg 21k .jpg file
The oak threshold is similar to this pic, so it extends down an extra half inch on the front. I have a hardwood flooring in the hallway (where the front of the threshold would sit on top of) and then a soft (ie somewhat thick) carpeting in the bedroom I am using the door for. My problem is, if I put the threshold so that the front part is sitting on top of the hardwood floor, the bottom of the door will probably be very high off the floor in the bedroom, since it will be propped up an extra half inch above the level of the wood floor, which is about the same height as the carpet, maybe slightly less. If i recess a notch in the wood floor (about a half inch deep before I hit asbestos laden tile), then the edge of the wood floor will be exposed, vulnerable to damage when stepped on, since the threshold would be sitting behind it, not on top of it.
I dont really care for the wood floor, it is a glueless, spongy floating floor that wasnt really installed professionally, but Id rather not crack it up if I can help it. And I dont have extra pieces laying around in case it does crack. Finally, how much of a gap should I leave between the header and top jamb? If I leave only half an inch, is that too tight as far as expansion/contraction and the fact I will have to make adjustments when I put the door in? I plan to fill that with non-expanding foam and acoustical sealant anyhow. Thanks for any input, much appreciated.